The purpose of this proposed research is to investigate the development of endocrine cardiovascular interactions in the mammalian fetus. This includes defining the basal plasma concentrations of the vasoactive peptides, angiotensin II and vasopressin, and of the catecholamines that exist in the fetus during the last month of gestation and in the neonate during the first two months after birth and correlating changes in these levels with changes in blood pressure and heart rate observed in these same animals during this period. Our goal is also to quantify, in a longitudinal study during late gestation, fetal cardiovascular (blood pressure, cardiac output, heart rate) and hormonal responses to a reduction in blood volume, and to assess the relative importance of vasopressin, angiotensin II and sympatho-adrenal activity in maintaining cardiovascular homeostasis during and after this stress at different times during gestation. The chronically cannulated ovine fetus is the animal model chosen for study. With this model it is possible to study endocrine-cardiovascular interactions in the absence of complications induced by the presence of anesthesia and surgical trauma, both of which are inherent in experiments on acutely prepared animals. These studies are necessary to define the maturational changes in endocrine-cardiovascular interrelationships that occur in the perinatal period. Such information will be useful in understanding the hormonal mechanisms important for the maintenance of fetal cardiovascular function during stress and may prove pertinent for clinical therapy in the premature infant or the term infant distress.